How do i remove a timemachine backup of the Applo Duo 2 timemachine volume

I have a Apollo Duo 2, what i use for timemachine, now i've noticed an old timemachine backup is still on the timemachine volume and i like to delete/remove it. But when i try in the finder, even with delete immidetly , it will not remove the timemachine backup. Is there an other way i can remove it?